It is our long term aim to determine the mechanism of developmentally programmed tissue regression in the mammalian eye. We will make extensive use of molecular and developmental research techniques to determine the mechanism of regression at both the cellular and molecular levels. We will use the pupillary membrane (PM) in the rodent eye as a model system in which to study tissue regression. The PM offers an ideal system for study since its regression occurs after birth in the mouse and rat, the PM is easily removed and visualized, and in general terms, the eye is accessible and non-essential. Specific aims: (1) To determine the mechanism of developmental tissue remodeling in the eye at the cellular level. In mammals, the macrophage has been implicated in tissue remodeling. Our preliminary data suggests that the hyalocyte, an ocular macrophage, is required for regression of the PM during development of the mouse eye. We will use both transgenic mice and intra-ocular injection as methods to prevent the action of hyalocytes in the eye during PM regression to confirm this result. These experiments will also allow us to determine whether the hyalocyte has an active or a passive role during tissue remodeling. Mast cell activities of will also be investigated since they are associated with the PM during its regression. (2) To determine whether regression of the PM involves apoptosis of the constituent cells. It will be determined whether a number of changes usually associated with apoptosis (such as the appearance of a nucleosomal ladder) occur in cells of the PM during regression. If apoptosis does occur during PM regression, it will imply, based on preliminary evidence, that the hyalocyte can induce apoptosis in target cells. (3) To identify cytokines that mediate the interaction between the hyalocytes and target structures during PM regression. To achieve this, we will determine whether previously recognized molecule's that are likely candidates for mediating a hyalocyte-target cell interaction are expressed with the appropriate pattern and timing. (4) To demonstrate, using an in vivo system, that the macrophage-target cell interaction is dependent upon the molecules identified in (3). We will use both transgenic mice and intra-ocular injection to introduce molecule-specific inhibitors and show they are required for remodeling ocular structures. The macrophage is a central player in many disease states including inflammatory disorders. Furthermore, it is required for normal immune function as well as wound healing, or "unscheduled" tissue -remodeling. Studying ocular tissue regression that is macrophage-mediated offers a unique opportunity to learn about the function of this cell in a normal process and potentially to apply the characteristic actions of macrophages in a therapeutic setting.